src/librustdoc/html/highlight.rs

   1 //! Basic syntax highlighting functionality.
   2 //!
   3 //! This module uses libsyntax's lexer to provide token-based highlighting for
   4 //! the HTML documentation generated by rustdoc.
   5 //!
   6 //! Use the `render_with_highlighting` to highlight some rust code.
   7
   8 use crate::html::escape::Escape;
   9
  10 use std::fmt::Display;
  11 use std::io;
  12 use std::io::prelude::*;
  13
  14 use rustc_parse::lexer;
  15 use syntax::token::{self, Token};
  16 use syntax::sess::ParseSess;
  17 use syntax::source_map::SourceMap;
  18 use syntax::symbol::{kw, sym};
  19 use syntax_pos::{Span, FileName};
  20
  21 /// Highlights `src`, returning the HTML output.
  22 pub fn render_with_highlighting(
  23     src: &str,
  24     class: Option<&str>,
  25     extension: Option<&str>,
  26     tooltip: Option<(&str, &str)>,
  27 ) -> String {
  28     debug!("highlighting: ================\n{}\n==============", src);
  29     let mut out = Vec::new();
  30     if let Some((tooltip, class)) = tooltip {
  31         write!(out, "<div class='information'><div class='tooltip {}'>ⓘ<span \
  32                      class='tooltiptext'>{}</span></div></div>",
  33                class, tooltip).unwrap();
  34     }
  35
  36     let sess = ParseSess::with_silent_emitter();
  37     let fm = sess.source_map().new_source_file(
  38         FileName::Custom(String::from("rustdoc-highlighting")),
  39         src.to_owned(),
  40     );
  41     let highlight_result = {
  42         let lexer = lexer::StringReader::new(&sess, fm, None);
  43         let mut classifier = Classifier::new(lexer, sess.source_map());
  44
  45         let mut highlighted_source = vec![];
  46         if classifier.write_source(&mut highlighted_source).is_err() {
  47             Err(())
  48         } else {
  49             Ok(String::from_utf8_lossy(&highlighted_source).into_owned())
  50         }
  51     };
  52
  53     match highlight_result {
  54         Ok(highlighted_source) => {
  55             write_header(class, &mut out).unwrap();
  56             write!(out, "{}", highlighted_source).unwrap();
  57             if let Some(extension) = extension {
  58                 write!(out, "{}", extension).unwrap();
  59             }
  60             write_footer(&mut out).unwrap();
  61         }
  62         Err(()) => {
  63             // If errors are encountered while trying to highlight, just emit
  64             // the unhighlighted source.
  65             write!(out, "<pre><code>{}</code></pre>", src).unwrap();
  66         }
  67     }
  68
  69     String::from_utf8_lossy(&out[..]).into_owned()
  70 }
  71
  72 /// Processes a program (nested in the internal `lexer`), classifying strings of
  73 /// text by highlighting category (`Class`). Calls out to a `Writer` to write
  74 /// each span of text in sequence.
  75 struct Classifier<'a> {
  76     lexer: lexer::StringReader<'a>,
  77     peek_token: Option<Token>,
  78     source_map: &'a SourceMap,
  79
  80     // State of the classifier.
  81     in_attribute: bool,
  82     in_macro: bool,
  83     in_macro_nonterminal: bool,
  84 }
  85
  86 /// How a span of text is classified. Mostly corresponds to token kinds.
  87 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
  88 enum Class {
  89     None,
  90     Comment,
  91     DocComment,
  92     Attribute,
  93     KeyWord,
  94     // Keywords that do pointer/reference stuff.
  95     RefKeyWord,
  96     Self_,
  97     Op,
  98     Macro,
  99     MacroNonTerminal,
 100     String,
 101     Number,
 102     Bool,
 103     Ident,
 104     Lifetime,
 105     PreludeTy,
 106     PreludeVal,
 107     QuestionMark,
 108 }
 109
 110 /// Trait that controls writing the output of syntax highlighting. Users should
 111 /// implement this trait to customize writing output.
 112 ///
 113 /// The classifier will call into the `Writer` implementation as it finds spans
 114 /// of text to highlight. Exactly how that text should be highlighted is up to
 115 /// the implementation.
 116 trait Writer {
 117     /// Called when we start processing a span of text that should be highlighted.
 118     /// The `Class` argument specifies how it should be highlighted.
 119     fn enter_span(&mut self, _: Class) -> io::Result<()>;
 120
 121     /// Called at the end of a span of highlighted text.
 122     fn exit_span(&mut self) -> io::Result<()>;
 123
 124     /// Called for a span of text. If the text should be highlighted differently from the
 125     /// surrounding text, then the `Class` argument will be a value other than `None`.
 126     ///
 127     /// The following sequences of callbacks are equivalent:
 128     /// ```plain
 129     ///     enter_span(Foo), string("text", None), exit_span()
 130     ///     string("text", Foo)
 131     /// ```
 132     /// The latter can be thought of as a shorthand for the former, which is
 133     /// more flexible.
 134     fn string<T: Display>(&mut self,
 135                           text: T,
 136                           klass: Class)
 137                           -> io::Result<()>;
 138 }
 139
 140 // Implement `Writer` for anthing that can be written to, this just implements
 141 // the default rustdoc behaviour.
 142 impl<U: Write> Writer for U {
 143     fn string<T: Display>(&mut self,
 144                           text: T,
 145                           klass: Class)
 146                           -> io::Result<()> {
 147         match klass {
 148             Class::None => write!(self, "{}", text),
 149             klass => write!(self, "<span class=\"{}\">{}</span>", klass.rustdoc_class(), text),
 150         }
 151     }
 152
 153     fn enter_span(&mut self, klass: Class) -> io::Result<()> {
 154         write!(self, "<span class=\"{}\">", klass.rustdoc_class())
 155     }
 156
 157     fn exit_span(&mut self) -> io::Result<()> {
 158         write!(self, "</span>")
 159     }
 160 }
 161
 162 enum HighlightError {
 163     LexError,
 164     IoError(io::Error),
 165 }
 166
 167 impl From<io::Error> for HighlightError {
 168     fn from(err: io::Error) -> Self {
 169         HighlightError::IoError(err)
 170     }
 171 }
 172
 173 impl<'a> Classifier<'a> {
 174     fn new(lexer: lexer::StringReader<'a>, source_map: &'a SourceMap) -> Classifier<'a> {
 175         Classifier {
 176             lexer,
 177             peek_token: None,
 178             source_map,
 179             in_attribute: false,
 180             in_macro: false,
 181             in_macro_nonterminal: false,
 182         }
 183     }
 184
 185     /// Gets the next token out of the lexer.
 186     fn try_next_token(&mut self) -> Result<Token, HighlightError> {
 187         if let Some(token) = self.peek_token.take() {
 188             return Ok(token);
 189         }
 190         let token = self.lexer.next_token();
 191         if let token::Unknown(..) = &token.kind {
 192             return Err(HighlightError::LexError);
 193         }
 194         Ok(token)
 195     }
 196
 197     fn peek(&mut self) -> Result<&Token, HighlightError> {
 198         if self.peek_token.is_none() {
 199             let token = self.lexer.next_token();
 200             if let token::Unknown(..) = &token.kind {
 201                 return Err(HighlightError::LexError);
 202             }
 203             self.peek_token = Some(token);
 204         }
 205         Ok(self.peek_token.as_ref().unwrap())
 206     }
 207
 208     /// Exhausts the `lexer` writing the output into `out`.
 209     ///
 210     /// The general structure for this method is to iterate over each token,
 211     /// possibly giving it an HTML span with a class specifying what flavor of token
 212     /// is used. All source code emission is done as slices from the source map,
 213     /// not from the tokens themselves, in order to stay true to the original
 214     /// source.
 215     fn write_source<W: Writer>(&mut self,
 216                                    out: &mut W)
 217                                    -> Result<(), HighlightError> {
 218         loop {
 219             let next = self.try_next_token()?;
 220             if next == token::Eof {
 221                 break;
 222             }
 223
 224             self.write_token(out, next)?;
 225         }
 226
 227         Ok(())
 228     }
 229
 230     // Handles an individual token from the lexer.
 231     fn write_token<W: Writer>(&mut self,
 232                               out: &mut W,
 233                               token: Token)
 234                               -> Result<(), HighlightError> {
 235         let klass = match token.kind {
 236             token::Shebang(s) => {
 237                 out.string(Escape(&s.as_str()), Class::None)?;
 238                 return Ok(());
 239             },
 240
 241             token::Whitespace | token::Unknown(..) => Class::None,
 242             token::Comment => Class::Comment,
 243             token::DocComment(..) => Class::DocComment,
 244
 245             // If this '&' or '*' token is followed by a non-whitespace token, assume that it's the
 246             // reference or dereference operator or a reference or pointer type, instead of the
 247             // bit-and or multiplication operator.
 248             token::BinOp(token::And) | token::BinOp(token::Star)
 249                 if self.peek()? != &token::Whitespace => Class::RefKeyWord,
 250
 251             // Consider this as part of a macro invocation if there was a
 252             // leading identifier.
 253             token::Not if self.in_macro => {
 254                 self.in_macro = false;
 255                 Class::Macro
 256             }
 257
 258             // Operators.
 259             token::Eq | token::Lt | token::Le | token::EqEq | token::Ne | token::Ge | token::Gt |
 260                 token::AndAnd | token::OrOr | token::Not | token::BinOp(..) | token::RArrow |
 261                 token::BinOpEq(..) | token::FatArrow => Class::Op,
 262
 263             // Miscellaneous, no highlighting.
 264             token::Dot | token::DotDot | token::DotDotDot | token::DotDotEq | token::Comma |
 265                 token::Semi | token::Colon | token::ModSep | token::LArrow | token::OpenDelim(_) |
 266                 token::CloseDelim(token::Brace) | token::CloseDelim(token::Paren) |
 267                 token::CloseDelim(token::NoDelim) => Class::None,
 268
 269             token::Question => Class::QuestionMark,
 270
 271             token::Dollar => {
 272                 if self.peek()?.is_ident() {
 273                     self.in_macro_nonterminal = true;
 274                     Class::MacroNonTerminal
 275                 } else {
 276                     Class::None
 277                 }
 278             }
 279
 280             // This might be the start of an attribute. We're going to want to
 281             // continue highlighting it as an attribute until the ending ']' is
 282             // seen, so skip out early. Down below we terminate the attribute
 283             // span when we see the ']'.
 284             token::Pound => {
 285                 // We can't be sure that our # begins an attribute (it could
 286                 // just be appearing in a macro) until we read either `#![` or
 287                 // `#[` from the input stream.
 288                 //
 289                 // We don't want to start highlighting as an attribute until
 290                 // we're confident there is going to be a ] coming up, as
 291                 // otherwise # tokens in macros highlight the rest of the input
 292                 // as an attribute.
 293
 294                 // Case 1: #![inner_attribute]
 295                 if self.peek()? == &token::Not {
 296                     self.try_next_token()?; // NOTE: consumes `!` token!
 297                     if self.peek()? == &token::OpenDelim(token::Bracket) {
 298                         self.in_attribute = true;
 299                         out.enter_span(Class::Attribute)?;
 300                     }
 301                     out.string("#", Class::None)?;
 302                     out.string("!", Class::None)?;
 303                     return Ok(());
 304                 }
 305
 306                 // Case 2: #[outer_attribute]
 307                 if self.peek()? == &token::OpenDelim(token::Bracket) {
 308                     self.in_attribute = true;
 309                     out.enter_span(Class::Attribute)?;
 310                 }
 311                 out.string("#", Class::None)?;
 312                 return Ok(());
 313             }
 314             token::CloseDelim(token::Bracket) => {
 315                 if self.in_attribute {
 316                     self.in_attribute = false;
 317                     out.string("]", Class::None)?;
 318                     out.exit_span()?;
 319                     return Ok(());
 320                 } else {
 321                     Class::None
 322                 }
 323             }
 324
 325             token::Literal(lit) => {
 326                 match lit.kind {
 327                     // Text literals.
 328                     token::Byte | token::Char | token::Err |
 329                     token::ByteStr | token::ByteStrRaw(..) |
 330                     token::Str | token::StrRaw(..) => Class::String,
 331
 332                     // Number literals.
 333                     token::Integer | token::Float => Class::Number,
 334
 335                     token::Bool => panic!("literal token contains `Lit::Bool`"),
 336                 }
 337             }
 338
 339             // Keywords are also included in the identifier set.
 340             token::Ident(name, is_raw) => {
 341                 match name {
 342                     kw::Ref | kw::Mut if !is_raw => Class::RefKeyWord,
 343
 344                     kw::SelfLower | kw::SelfUpper => Class::Self_,
 345                     kw::False | kw::True if !is_raw => Class::Bool,
 346
 347                     sym::Option | sym::Result => Class::PreludeTy,
 348                     sym::Some | sym::None | sym::Ok | sym::Err => Class::PreludeVal,
 349
 350                     _ if token.is_reserved_ident() => Class::KeyWord,
 351
 352                     _ => {
 353                         if self.in_macro_nonterminal {
 354                             self.in_macro_nonterminal = false;
 355                             Class::MacroNonTerminal
 356                         } else if self.peek()? == &token::Not {
 357                             self.in_macro = true;
 358                             Class::Macro
 359                         } else {
 360                             Class::Ident
 361                         }
 362                     }
 363                 }
 364             }
 365
 366             token::Lifetime(..) => Class::Lifetime,
 367
 368             token::Eof | token::Interpolated(..) |
 369             token::Tilde | token::At| token::SingleQuote => Class::None,
 370         };
 371
 372         // Anything that didn't return above is the simple case where we the
 373         // class just spans a single token, so we can use the `string` method.
 374         out.string(Escape(&self.snip(token.span)), klass)?;
 375
 376         Ok(())
 377     }
 378
 379     // Helper function to get a snippet from the source_map.
 380     fn snip(&self, sp: Span) -> String {
 381         self.source_map.span_to_snippet(sp).unwrap()
 382     }
 383 }
 384
 385 impl Class {
 386     /// Returns the css class expected by rustdoc for each `Class`.
 387     fn rustdoc_class(self) -> &'static str {
 388         match self {
 389             Class::None => "",
 390             Class::Comment => "comment",
 391             Class::DocComment => "doccomment",
 392             Class::Attribute => "attribute",
 393             Class::KeyWord => "kw",
 394             Class::RefKeyWord => "kw-2",
 395             Class::Self_ => "self",
 396             Class::Op => "op",
 397             Class::Macro => "macro",
 398             Class::MacroNonTerminal => "macro-nonterminal",
 399             Class::String => "string",
 400             Class::Number => "number",
 401             Class::Bool => "bool-val",
 402             Class::Ident => "ident",
 403             Class::Lifetime => "lifetime",
 404             Class::PreludeTy => "prelude-ty",
 405             Class::PreludeVal => "prelude-val",
 406             Class::QuestionMark => "question-mark"
 407         }
 408     }
 409 }
 410
 411 fn write_header(class: Option<&str>, out: &mut dyn Write) -> io::Result<()> {
 412     write!(out, "<div class=\"example-wrap\"><pre class=\"rust {}\">\n", class.unwrap_or(""))
 413 }
 414
 415 fn write_footer(out: &mut dyn Write) -> io::Result<()> {
 416     write!(out, "</pre></div>\n")
 417 }